MCDANIEL TANK RHYOLITE


The McDaniel Tank Rhyolite obsidian source, discovered by Jeff Ferguson (Missouri Research Reactor Center), is part of the Squaw Peak Volcanic Center, identified and described by Bobrow (1983; see also Bobrow et al. 1983). The Squaw Peak Center is in the far northeastern portion of the Mogollon-Datil Volcanic Province dated between about 35 and 20 Ma (Shackley et al. 2017).  The Squaw Peak Volcanic center is comprised of three distinct mid-to-late Tertiary (Neogene) rhyolite domes, the oldest is the flow banded phenocryst poor, high-K, high SiO2 rhyolite tephra that covers much of the northern part of Squaw Peak and north that includes McDaniel Tank dated by K-Ar to 18.3 0.7 Ma (Bobrow 1983:15; see image below). The tuff is characterized as a dark brown to black, welded, basal ash flow tuff overlain, in parts, by a folded lithoidal lava. Obsidian was not recorded by Bobrow.  The marekanites appear to be lava fragments quenched during the ash flow eruptive event. Field survey during August of 2012 indicated outcrops of marekanite clusters at various points in the 4.1 km3 tuff volume, although the distribution of the ash flow seems larger than that recorded by Bobrow (Bobrow 1983:15). While the volume is relatively low, the area covered is quite large given the relatively thin depth of the ash flow as seen in 2012.

Analysis by XRF and NAA by Bobrow (1983) indicates a relatively close similarity between the major, minor, and trace elements between his sample of rhyolite lava and the obsidian given the expected differences between a crystalline rhyolite and glass (see Bobrow et al. 1983:215). 

Table 1.  Elemental concentrations for the McDaniel Tank Rhyolite obsidian source standards, mean values for Bobrow et al. (1983) rhyolite analysis, and USGS RGM-1 rhyolite standard.  All measurements in parts per million (ppm). n.r.=no report

 

 

SAMPLE

Ti

Mn

Fe

Zn

Rb

Sr

Y

Zr

Nb

Ba

Pb

Th

082812-1-1

1735

538

11701

67

158

183

36

251

41

1431

19

26

2

1817

527

12072

68

165

190

40

263

43

1553

20

24

3

1914

537

12744

82

160

191

38

261

37

1459

18

15

4

1974

515

12592

70

166

190

35

269

40

1499

22

19

5

1830

544

12842

74

159

189

42

257

40

1481

19

23

6

1767

533

11873

65

159

185

36

260

38

1420

20

21

7

1809

493

12444

71

157

184

36

260

40

1435

18

17

8

1758

468

11871

64

145

179

33

252

39

1377

17

14

9

1894

577

12568

70

170

204

37

278

45

1586

25

20

10

2030

578

12942

84

159

186

39

253

36

1394

21

28

11

1779

509

11966

66

155

179

38

259

40

1481

20

21

12

1695

488

11453

61

148

181

35

258

40

1469

20

17

13

1855

481

11763

69

153

182

37

259

38

1150

18

18

14

1880

550

13146

82

162

188

37

254

38

1426

21

20

15

1986

561

13470

68

159

190

37

257

37

1434

19

18

16

1996

542

12748

71

160

192

39

274

42

1564

20

20

17

1963

538

13338

71

160

193

37

273

39

1561

19

20

18

1827

542

12665

78

159

183

37

257

38

1471

19

18

19

1683

532

11994

69

154

185

40

260

42

1483

19

17

Bobrow et al. (1983) mean value n.r. n.r. n.r. n.r. 170 134 43 255 43 n.r. 24 24

RGM1-S4

1634

286

13399

41

152

110

25

213

9

849

22

9

 

 

Table 2. Mean and central tendency for the data in Table 1.

 

 

 

 

 

 

 

 

 

 

Table 3.  Major and minor oxides for one sample of McDaniel Tank obsidian, Bobrow et al. (1983) analysis of a McDaniel Tank rhyolite sample, and USGS RGM-1 rhyolite standard.

Sample

SiO2

Al2O3

CaO

Fe2O3T

K2O

MgO

MnO

Na2O

TiO2

McDaniel Tank, NM

 

 

 

 

 

 

 

 

 

082812-1-1

76.01 12.158 1.143 1.60 4.758 0.11 0.083 3.44 0.247
Bobrow et al. (1983) analysis 73.95 14.24 0.09 1.231 4.55 0.23 0.08 4.52 0.25

RGM1-S4 USGS standard

73.73

13.190

1.3998

2.221

4.900

<.001

0.0403

4.01

0.237

1 FeO 

 

Figure 1.  The northeastern Mogollon-Datil Volcanic Province volcanic centers (from Bobrow 1984)


 

REFERENCES

Bobrow, D.J. 1984, Geochemistry and petrology of Miocene silicic lavas in the Socorro-Magdalena area of New Mexico.  Master's thesis, Department of Geology, New Mexico Institute of Mining and Technology, Socorro.

Bobrow, D.J., P.R. Kyle, and G.R. Osburn, 1983, Miocene rhyolitic volcanism in the Socorro Area of New Mexico.  In C.E. Chapin (Ed.) Socorro Region II, New Mexico Geological Society 34th Annual Field Conference, pp. 211-218. New Mexico Institute or Mining and Technology, Socorro.

Shackley, M.S., L.E. Morgan, and D. Pyle, 2017, Elemental, isotopic, and geochronological variability in Mogollon-Datil Volcanic Province archaeological obsidian, Southwestern New Mexico: solving issues of inter-source discrimination.  Geoarchaeology, in press.

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